If a conventional method for culturing microorganisms is explained while taking the determination of the total viable count in the food test by way of example, dehydrated agar medium is first dissolved and sterilized and then maintained at a temperature of about 45.degree. C. A predetermined amount of the agar medium is dispensed in, for instance, sterilized Petri dishes to which a constant amount of a sample such as a suspension of a food is previously added, followed by pour culture thereof, solidification of the agar, culturing at a constant temperature and counting the number of developed colonies of microorganisms. Thus, the conventional method for culturing microorganisms requires much time and labor since, in the method, a culture medium must preliminarily be prepared, sterilized and then maintained at a temperature at which the medium is not solidified. In addition, the method in general uses a large number of plastic Petri dishes and therefore, generates a large amount of plastic waste. To easily and rapidly carry out bacteriological tests, it is preferred to develop a method which permits the omission of the preparation of such a culture medium which requires much time and labor and is accompanied by the generation of a lesser amount of plastic waste.
Moreover, an environmental test in general comprises the steps of wiping a predetermined area of a subject to be tested with, for instance, a swab; dipping the swab with sterilized water or physiological saline so that the bacterial cells adhered to the swab are suspended in the sterilized water or physiological saline; inoculating an agar medium preliminarily prepared with the suspension or culturing the bacterial cells according to the pour plate method similar to that used above; and then testing the bacterial cells and determining the viable counts.
There have already been put on the market several types of simplified culture media which are designed such that it is easy to handle and is fit for various purposes. These commercially available simplified culture media may be classified for convenience into, for instance, stamp type one (Japanese Un-Examined Patent Publication (hereinafter referred to as "J. P. KOKAI") No. Hei 4-117299); filter-type and film-type ones (Japanese Examined Patent Publication (hereinafter referred to as "J. P. KOKOKU") No. Hei 2-49705 and J. P. KOKAI No. Hei 3-15379); and test paper-type one.
When using the stamp-type culture medium, the bacteriological test is carried out by dispensing an agar medium in plastic containers to such an extent that the medium stands up above the rim of the container, directly bringing the surface of the agar medium into contact with a subject to be tested to thus inoculate the medium with microorganisms and culturing the microorganisms. This culture medium may easily be used for briefly testing the contamination of environment with microorganisms, but this test is insufficient in quantitativeness because of a small area size of the medium and it is difficult to test a subject having a curved and/or uneven surface using the medium. Moreover, the method also suffers from a problem in that the culture medium is directly brought into contact with a subject to be tested and therefore, the method is not used for the test of, for instance, foods. In addition, the method uses plastic Petri dishes and therefore, generates a large amount of plastic waste after the culturing, like the foregoing conventional method. The filter-type culture medium is suitable for the test of liquid samples, but is not easily used for the test of samples other than liquids. The test paper-type culture medium suffers from a problem in that it does not permit any quantitative analysis. The film-type culture medium can easily be applied to the food test since the medium permits a quantitative analysis, but when it is used for the environmental test, the medium cannot directly come in contact with a subject to be tested unlike the stamp-type one.
As has been discussed above, there have been proposed several types of commercially available simplified culture media, but none of them have presently been able to be used, alone, in various applications such as food tests, tests of liquid samples, tests in which the medium directly comes in contact with a subject to be tested.